Digital signal recording method and digital video tape recorder

ABSTRACT

A digital video tape recorder has interpolation and crossfading circuits and records audio and video signals in independent frames, the audio frames being offset with respect to the video frames. For a four-channel audio signal, the even and odd samples are recorded near different edges of the tape, enabling burst errors near one edge to be recovered efficiently by Interpolating the audio signal from the other edge. When audio dubbing is performed, the first and last dubbed frames contain the even samples of the new signal and the odd samples of the old signal, or vice versa, and audio-dubbing flags are recorded in the these frames. When these frames are played back, the old and new signals are regenerated by interpolation and crossfaded to create a smooth transition between them. The same apparatus can also be used to record a two-channel signal, by recording each sample twice.

This application is a continuation of application Ser. No. 07/362,243filed on Jun. 6, 1989, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a method of recording digital audio and videosignals on a magnetic tape, and to a digital video tape recorder forrecording signals according to this method and playing back the recordedsignals.

Video tape recorders, also known as video cassette recorders, are widelyused both in the television broadcast industry and at the consumer levelfor recording and playing back video signals with associated audiosignals. The audio and video signals are recorded on a magnetic tape ina series of helical tracks oriented at an angle to the long axis of thetape. Recently digital video tape recorders, which offer superior noiseperformance and editing capabilities, have come into use. In recording,a digital video tape recorder samples analog audio and video inputsignals, encodes the sample values digitally, and records the digitaldata on the tape. In playback, the digital video tape recorder readsdigital data from the tape, decodes the data, and generates analog audioand video output signals.

The prior art of recording digital audio and video signals is embodiedin, for example, the D-2 format developed by the Society of MotionPicture and Television Engineers, in which each helical track comprisesa video sector and two short audio sectors, the audio sectors beingdisposed at the two ends of the track. The audio sectors are thuslocated near the edges of the tape, which are the areas most prone toburst errors caused by scratches. Various error countermeasures aretaken. For example, an error-correcting code is recorded together withthe audio and video data, permitting the correction of burst errors upto a certain length. Also, the audio signal, which normally comprisesfour channels, is recorded with 100% redundancy, identical data beingwritten in the audio sectors at the upper and lower edges of the tape.

The video signal is divided into frames, a frame corresponding to onecomplete image on the screen. A frame is divided into two fieldscomprising the even and odd raster lines on the screen, respectively. Inthe D-2 format, a frame comprises twelve consecutive helical tracks onthe tape, each of its constituent fields comprising six consecutivetracks.

The audio signal is recorded in a continuous manner without beingdivided into frames and fields in any special way on the tape. Mostdigital video tape recorders, however, internally divide the audiosignal into frames at the same points as the video signal and processthe audio signal one frame at a time.

When a tape is edited, the editing normally begins and ends at aboundary between video frames, which provides a clean break in the videoimage. This practice is generally followed even when the editing isaudio dubbing, in which the video signal is left unchanged but the audiosignal is replaced with a new audio signal. In the prior art, since thesame frame boundaries are used For the audio and video signals, afteraudio dubbing each audio frame consists entirely of the old audio signalor entirely of the new audio signal.

One problem with the D-2 format is that it adopts an inefficient meansof coping with burst errors: recording the audio signal with 100%redundancy uses excessive space on the tape. This problem becomes evenmore pronounced when the D-2 format is adapted to a two-channel audiosignal. (Many digital video tape recorders are built to accept bothtwo-channel and four-channel audio signals.) If the same recordingparameters (such as sampling frequency and number of bits per sample)are used as for a four-channel signal, the D-2 format requires 200%redundancy for a two-channel signal.

A further problem is that, the question of redundancy aside, thedisposition of the audio sectors in narrow strips near the edges of thetape increases their vulnerability to burst errors, while the relativeshortness of the audio sectors limits the error-correcting capability ofthe error-correcting code.

A problem that occurs when audio dubbing is performed using the D-2format is that, while a clean break may be desirable in the videosignal, it causes noise in the audio signal. Irritating clicks are heardat the points of change from the old audio signal to the new audiosignal and from the new audio signal to the old audio signal. (Thesepoints will be referred to herein as the edit points.) Complex schemeshave been used to combat this edit-point noise, but without completesuccess.

SUMMARY OF THE INVENTION

One object of the present invention is accordingly to provide efficientprotection against burst errors.

Another object is to enable two-channel and four-channel audio signalsto be recorded efficiently according to the same parameters.

Yet another object is to enable an audio-dubbed tape to be played backwithout unwanted audio noise at the edit points.

A digital signal recording method for recording digital audio and videosignals in helical tracks on a tape according to this inventioncomprises steps of recording the video signal in video sectors in thehelical tracks, separating the even samples of the audio signal from theodd samples, recording the even samples in audio sectors disposed nearone edge of the tape, and recording the odd samples in audio sectorsdisposed near the other edge of the tape.

If the audio signal has two channels, the steps of recording the evenand odd samples of the audio signal are repeated so that each sample isrecorded twice in different audio sectors disposed near opposite edgesof the tape.

The audio and video signals are furthermore divided into independentframes, the boundaries of the audio frames being offset from theboundaries of the video frames, and the even and odd samples in an audioframe are recorded in different helical tracks, these being located indifferent video frames. When audio dubbing is performed, anaudio-dubbing flag is recorded in at least the first and last dubbedaudio frames.

A digital video tape recorder according to this invention comprises arecording audio digital signal processing circuit for separating theeven and odd samples of the audio signal when they are recorded on thetape, a sequence circuit for adding an audio-dubbing flag andinformation indicating the number of channels in the recorded audiosignal, and a playback audio digital signal processing circuit with adecoding circuit, an ID detection circuit, one or more interpolationcircuits for interpolating even and odd samples on command from the IDdetection and decoding circuits, and one or more crossfading circuitsfor crossfading the audio signal when the ID detection circuit detectsan audio-dubbing flag.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a tape with helical tracks, illustrating a prior-artdigital signal recording method.

FIG. 2 shows the tracks in FIG. 1 rearranged to illustrate theirscanning sequence.

FIG. 3 shows the channel structure of the audio sectors in FIG. 1.

FIG. 4 shows the data structure of the audio sectors in FIG. 1.

FIG. 5 shows the error-correcting code structure of the audio sectors inFIG. 1.

FIG. 6 illustrates the error-correcting capability of theerror-correcting code structure in FIG. 5.

FIGS. 7A and 7B illustrate the effect of audio dubbing the prior art.

FIG. 8 shows a tape with helical tracks illustrating the novel digitalsignal recording method.

FIG. 9 shows the tracks in FIG. 8 rearranged to illustrate theirscanning sequence.

FIG. 10 shows the channel structure of the audio sectors in FIG. 8 forthe four-channel case.

FIG. 11 shows the channel structure of the audio sectors in FIG. 8 forthe two-channel case.

FIG. 12 shows a first example of the data structure of the audio sectorsin FIG. 8.

FIG. 13 shows the structure of an audio subsector in FIG. 12 containingeven sample data.

FIG. 14 shows the structure of an audio subsector in FIG. 12 containingodd sample data.

FIG. 15 shows a second example of the data structure of the audiosectors in FIG. 8.

FIG. 16 shows the error-correcting code structure of the second examplein greater detail.

FIG. 17 illustrates the error-correcting capability of theerror-correcting code structure in FIG. 16.

FIG. 18A and FIG. 18B illustrate the effect of audio dubbing in thenovel method for the four-channel case.

FIG. 19A and FIG. 19B illustrate the effect of audio dubbing in thenovel method for the two-channel case.

FIG. 20 is a block diagram of a novel digital video tape recorder.

FIG. 21 is a more detailed block diagram of the playback audio digitalsignal processing circuit in FIG. 20.

FIG. 22 is a timing chart illustrating the audio dubbing process.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A novel method of recording digital audio and video signals on magnetictape, and a video tape recorder employing this method, will be describedwith reference to the drawings. First, however, a more detaileddescription will be given of the prior-art method as embodied in the D-2format.

FIG. 1 shows a tape 1 on which audio and video signals are recorded onhelical tracks 2 according to the D-2 format. Each helical track 2comprises a video sector 3, an upper tape edge audio sector 4, and alower tape edge audio sector 5. The twelve tracks illustrated in thedrawing make up one signal frame, the frame comprising two fields of sixtracks each. The tracks are further grouped into segments, eachcomprising a pair of adjacent tracks. During recording or playback, thetwo tracks in a segment are scanned simultaneously as will be explainedlater.

FIG. 1 is schematic in nature and does not represent the actualappearance of the tape. For example, cue, control, and time codeinformation is recorded in linear tracks disposed at the edges of thetape, which are not shown in the drawing. Also, for convenience ofillustration the helical tracks 2 are shown inclined more steeply thanthey actually are. The actual helical track angle is approximately 6°.

FIG. 2 is a schematic drawing in which the tracks in FIG. 1 have beenrearranged to show more clearly the sequence in which they are scanned.The upper and lower rows of tracks are scanned simultaneously. A segmentcomprises a pair of vertically adjacent tracks in FIG. 2, a fieldcomprises three consecutive segments, and a frame comprises a pair ofconsecutive fields.

FIG. 3 shows the structure of the audio sectors 4 and 5 further detail.Each audio sector 4 or 5 is divided into a pair of subsectors 10. When afour-channel signal is recorded, the data for each channel is recordedtwice in each segment: once in a subsector of an upper tape edge audiosector 4, and once in a subsector of a lower tape edge audio sector 5.

FIG. 4 shows the structure of the audio sectors in still further detail.The subsectors 10 are delimited from each other and from the videosector 3 by gaps 11, which physically separate the subsectors andprovide space for the recording of preamble and postamble information.Each subsector 10 comprises twelve data blocks 12, numbered #0 to #11.Each data block in turn comprises a header 13, a pair data or C2 fields14 in which either data or an outer error-correcting code is recorded,and a pair of C1 fields 15 in which an inner error-correcting code isrecorded. The header 13 comprises a synchronization field 16 in which asynchronization pattern is recorded, and an ID field 18 in which userinformation such as a program index number can be recorded. Thesynchronization field 16 comprises two bytes, or "symbols," of data, theID field 18 comprises two bytes, the data or C2 fields 14 compriseeighty-five bytes each, and the C1 fields 15 comprise eight bytes each.

At normal audio sampling rates of, For example, 800 samples per fieldwith 16 to 20 bits per sample, the data capacity of the D-2 audiosectors greatly exceeds the actual amount of audio sample data. Theexcess space is used for recording data other than audio sample data, oris left unused.

FIG. 5 is a schematic diagram illustrating the structure of an audiosubsector 10 in a way that explicates the operation of theerror-correcting code, omitting the headers 13. The data and C2 fields14 contain audio data in eight of the twelve data blocks 12 and outercodes C2 in the remaining four blocks. The error-correcting code is ofthe Reed-Solomon type, in which the inner code C1 enables the correctionof errors within blocks, and the outer code C2 enables the correction oferrors extending across blocks. The assignment of an eight-byte innercode C1 to each eighty-five data bytes enables the correction of dataerrors in up to three of the eighty-five bytes. In the across-blockdirection, the assignment of four outer code bytes C2 to each eightaudio data bytes, combined with erasure flags generated from the innercode C1, enables the correction of data errors in up to four of theeight data bytes.

FIG. 5 corresponds to the storage structure that would normally beemployed in the memory of a digital video tape recorder, not thephysical structure on the tape. On the tape, the data blocks 12containing outer error-correcting codes C2 are interleaved among thedata blocks 12 containing data.

FIG. 6 shows the error-correcting capability of the D-2 format in termsof physical dimensions on the tape. Burst errors can be corrected if therange of the error does not exceed 1.3 mm in the direction parallel tothe track, which corresponds to a scratch parallel to the tape axis witha maximum length of 1.29 mm or a maximum height of 0.14 mm.

FIGS. 7A and 7B illustrate the effect of audio dubbing in the D-2format. FIG. 7A illustrates a three-field portion of the old audiosignal, wherein the first two fields (O and A) belong to a frame V, thiscorresponding to a frame of the video signal, and the next field (B) isthe first field in the next frame. Audio dubbing begins at the end ofthe frame V; that is, at the boundary between fields A and B. Thus a newsignal, represented by black dots in FIG. 7B is recorded over the oldsignal starting in field B. The result, as shown In FIG. 7B, Is adiscontinuity in the audio signal that causes audible noise.

A novel method of recording audio and video signals on a magnetic tapewill next be explained with reference to FIGS. 8 to 17. The novel methoddiffers from the prior art in using fewer audio sectors, employing lessredundancy, dividing the audio signal into frames that are offset fromthe video frames, and recording even and odd samples of the audio signalat different edges of the tape.

FIG. 8 shows a tape 1 on which audio and video signals are recorded inhelical tracks 2 according to the novel method. The tracks are pairedinto segments and grouped into fields of three segments each as in theprior art, the segment and field groupings being common to the audio andvideo signals. The video signal is divided into frames comprising twofields each. The audio signal is also divided into frames comprising twofields each, but the boundaries between audio frames are offset by onefield from the boundaries between video frames. Thus a pair of fieldsdisposed in the same audio frame are disposed in different video frames,and vice versa.

The video signals are recorded in video sectors 23. The audio signalsare recorded in upper tape edge audio sectors 24 and lower tape edgeaudio sectors 25. In the novel method, audio sectors 24 and 25 arerecorded in a subset of the tracks in a frame, not In every track. InFIG. 8, for example, upper tape edge audio sectors 24 are recorded inonly one of the six segments in a frame, and lower tape edge sectoraudio sectors 25 are recorded in another one of the six segments. Theupper tape edge audio sectors 24 are disposed in different fields fromthe lower tape edge audio sectors 25.

As in the prior art, there may also be linear cue, control, and timecode tracks disposed at the edges of the tape, not shown in the drawing,and the actual helical track angle is substantially 6°.

FIG. 9 is a schematic diagram in which the tracks have been rearrangedto show more clearly the order in which they are scanned. The upper andlower rows of tracks in FIG. 9 are scanned simultaneously. The audiosignal in an audio frame is recorded in a pair of upper tape edge audiosectors 24 disposed at one end of the audio frame, and a pair of lowertape edge audio sectors 25 disposed at the other end. This dispositionis preferable because it enables a group of four audio sectors disposedat the middle of a video frame to be scanned contiguously.

FIG. 10 shows how a four-channel audio signal is recorded in the twoupper tape edge audio sectors 24 and the two lower tape edge audiosectors 25 in one audio frame. Each audio sector 24 or 25 comprises apair of audio subsectors 30, which are separated from each other andfrom the video sectors 23 by gaps 31 similar to the gaps 11 employed inthe prior art. Each audio subsector 30 contains audio data representingeither even-numbered samples or oddnumbered samples of the audio signalin one channel. The four audio channels are assigned to audio subsectors30 as shown, the even samples of each channel being recorded in theupper tape edge audio sectors 24 and the odd samples in the lower tapeedge audio sectors 25. The even and odd samples are thus recorded indifferent fields in the audio frame.

Since a four-channel audio signal is recorded without redundancy, ituses tape space more efficiently than in the prior art. Protectionagainst burst errors is provided by recording the even and odd signalsat different edges of the tape, so that if a burst error destroys thedata at one edge of the tape, a digital video tape recorder can stillrecover the data at the other edge and restore the original audio signalby interpolation, with little or no perceptible degradation of soundquality. The protection afforded by separating the even and odd signalis thus substantially equivalent to the protection provided by 100%redundancy in the prior art.

For protection against burst errors occurring simultaneously at bothedges of the tape, in the upper tape edge audio sectors 24 channels 2and 4 are recorded in the outermost audio subsectors 30, these being theones most vulnerable to burst errors, while in the lower tape edgesectors 25 channels 1 and 3 are recorded in the outermost audiosubsectors 30. This reduces the probability that the signal for a givenchannel will be lost completely.

FIG. 11 shows how a two-channel audio signal is recorded according tothe novel method. The signal for each channel is recorded twice: oncewith the even samples in an upper tape edge audio sector 24 and the oddsamples in a lower tape edge audio sector 25; and once with the evensamples in a lower tape edge audio sector 25 and the odd samples in anupper tape edge audio sector 24. The entire signal can thus be recoveredfrom either edge of the tape. A two-channel signal therefore enjoys evenbetter protection against burst errors than a four-channel signal.

Next two examples of data structures that can be employed in the audiosubsectors 30 of the novel method will be described with reference toFIGS. 12 to 16.

In the first example, shown in FIG. 12, an audio subsector 30 comprisesforty-eight data blocks 32, numbered #0 to #47. Each data block in turncomprises a header 33, a data or C2 field 34 in which either data or anouter error-correcting code is recorded, and a C1 field 35 in which atwo-byte inner error-correcting code is recorded. The header 33comprises a synchronization field 36, an address field 37, an ID field38, and a parity field 39. The synchronization field 36 comprises atwo-byte synchronization pattern. The address field 37 comprises aone-byte block address specifying, for example, the block sequencenumber. The one-byte ID field comprises user information such as aprogram number, and flags indicating whether the audio signal has two orfour channels and whether it has been recorded normally or by audiodubbing. The parity field 39 comprises a one-byte error-correcting codefor the header. The data or C2 field 34 comprises forty bytes and isthus capable of storing, For example, twenty 16-bit digitized signalsamples.

FIG. 13 shows the audio subsector structure in more detail for the casein which the sampling rate is eight hundred 16-bit samples per field, or1600 samples per audio frame, the samples being numbered from 0 to 1599.The audio subsector in FIG. 13 contains even sample data. The headers 33are not shown. The structure is interleaved in the following manner.Data blocks #0, #2, . . . , #18 contain audio signal samples 0, 8, . . .; data blocks #24, #26, . . . , #42 contain samples 2, 10, . . . ; datablocks #1, #3, . . . , #19 contain samples 4, 12, . . . ; data blocks#25, #27, . . . , #43 contain samples 6, 14, . . . . Data blocks #20 to#23 and #44 to #47 contain outer (C2) error correcting codes.

FIG. 14 shows the structure of an audio subsector in which odd samplesare recorded. The data is interleaved in the same way as in FIG. 13,only the sample numbers being different.

The effect of the Interleaving in FIGS. 13 and 14 is to distribute thedamage caused by a burst error over different parts of the audio signalso that even if the error cannot be corrected by the error-correctingcodes, the resulting degradation of the audio sound will be lessperceptible than if the error were concentrated at one place. Thisinterleaving and the separation of odd and even samples at differentedges of the tape provides adequate protection against burst errors withless error-correcting code information than the prior art and noredundancy, thus enabling the audio signal to be recorded much moreefficiently than in the prior art.

The second example, shown in FIG. 15, also enables the audio signal tobe recorded more efficiently than in the prior art, and provides evengreater protection against burst errors. In this example a subsector 30comprises thirty data blocks 42 numbered #0 to #29. Each data block 42comprises a five-byte header 43, an eighty-byte data or C2 field 44, andan eight-byte C1 field. The header 43 is similar in structure to theheader 33 in FIG. 12, comprising a synchronization field 46, an addressfield 47, an ID field 48, and a parity field 49.

FIG. 16 shows the audio subsector structure in FIG. 15 in a differentform, omitting the headers 43. Audio sample data is stored in twenty ofthe data blocks, and outer (C2) error-correcting codes in ten of thedata blocks. The data blocks and data samples can be interleaved in away similar to that shown in FIGS. 13 and 14. The C1 error-correctingcodes enable the correction of in-block errors up to three bytes inlength. The C2 error-correcting codes, providing ten bytes oferror-correcting information for each twenty bytes of data, enable thecorrection of up to four-byte errors in the across-block direction.

FIG. 17 shows this error-correcting capability in terms of physicaldimensions on the tape. The error-correcting codes in FIGS. 15 and 16can correct burst errors extending up to 3.9 mm in the directionparallel to the track, corresponding to a scratch parallel to the tapeaxis with a maximum length of 3.87 mm or a maximum height of 0.42 mm.This improvement by a factor of 3.0 over the prior art results from theuse of longer audio subsectors.

From the foregoing description it will be apparent that time novelrecording method enables both two-channel and four-channel audio signalsto be recorded with the same parameters, requiring only substantiallyhalf as much space as in the prior art, or less. Efficient errorprotection strategies such as separating the even and odd samples,however, enable the novel method to provide adequate protection againstburst errors, the degree of protection in the second example shown FIGS.15 to 17 exceeding that in the prior art.

In addition to protecting against burst errors, the novel method alsoenables noise introduced at the edit points by audio dubbing to beprevented. This is done by recording an audio-dubbing flag in the IDfield 38 or 48 to indicate where audio dubbing is performed, so that adigital video tape recorder equipped with a crossfading circuit cancrossfade the old and new audio signals at the edit points. FIGS. 18Aand 18B illustrate this process for a four-channel audio signal.

FIG. 18A shows three fields of the old audio signal, fields O and Abelonging to one video frame and field B to the next video frame. Sluicethe audio and video frames are staggered, fields A and B are in the sameaudio frame. Hence the even samples of the signal in this audio frame,represented by white circles, are recorded in field A and the oddsamples, represented by black circles, in field B.

Audio dubbing begins as usual at the end of a video frame, in this caseat the end of field A, this point being marked as the edit point e. Theaudio signal in field B is replaced with a new audio signal labeled Y inFIG. 18B. The data in the audio frame at the edit point e thereforecomprises the even samples of the old audio signal recorded in field A,and the odd samples of the new audio signal recorded in the field nowlabeled Y. In addition an audio-dubbing flag is recorded as IDinformation in one or more data blocks in field Y.

When the edited tape is played back, the digital video tape recorder candetect the audio-dubbing flag in the audio frame comprising fields A andY, regenerate the old audio signal by interpolation from the evensamples in field A, regenerate the new audio signal by interpolationfrom the odd samples in field Y, and crossfade the old and new audiosignals during the playback process. The result will be the audio outputsignal shown at the bottom of FIG. 18B, in which a smooth, noise-freetransition occurs from the old audio signal to the new audio signal.

FIGS. 19A and 19B illustrate the same process for a two-channel audiosignal. In this case, the same audio information is recorded in fields Aand B in FIG. 19A. After audio dubbing, the digital video tape recordercan obtain the entire old audio signal from field A, and the entire newaudio signal from field Y; it can therefore crossfade these signalswithout the need for interpolation.

A similar procedure is followed at the edit point at the end of audiodubbing. An audio-dubbing flag is recorded as ID information in the lastaudio field to be dubbed. During playback, the audio signal from thisfield is crossfaded with the audio signal from the next field, whichbelongs to the same audio frame, to create a smooth transition from thenew to the old signal.

Next a novel video tape recorder for recording digital audio and videosignals on a magnetic tape by the novel method and playing them backwill be described with reference to FIGS. 20 to 22. The novel video taperecorder employs well-known circuits such as modulating, mixing,demodulating, separation, decoding, interpolation, and crossfadingcircuits, detailed descriptions of the internal structure of which willbe omitted.

FIG. 20 is a block diagram illustrating the overall structure of thenovel digital video tape recorder. The recording section 80 has fouraudio input terminals: a channel-1 audio signal input terminal 101, achannel-2 audio signal input terminal 102, a channel-3 audio signalinput terminal 103, and a channel-4 audio signal input terminal 104. Theaudio signals input at these terminals are applied respectively to afirst analog-to-digital (hereinafter written A/D) converter 105 forconverting the channel-1 audio signal to a digital signal, a similarsecond A/D converter 106, a similar third A/D converter 107, and asimilar fourth A/D converter 108. The outputs of the third and fourthA/D converters 107 and 108 are sent through a firstnumber-of-recording-channels switch 109 and a secondnumber-of-recording-channels switch 110, respectively, to a recordingaudio digital signal processing circuit 111, while the outputs of thefirst and second A/D converters 105 and 106 are sent directly to therecording audio digital signal processing circuit 111. The recordingaudio digital signal processing circuit 111 also receives ID informationfrom a sequence circuit 112.

The recording section also comprises a video signal input terminal 113connected to a fifth A/D converter 114, the output of which is sent to arecording video digital signal processing circuit 115. A mixing circuit116 receives the output of the recording audio digital signal processingcircuit 111 and the recording video digital signal processing circuit115 and combines them by time-division multiplexing. The output of themixing circuit 116 is routed over two paths: one leading to a firstmodulating circuit 117 for modulating the multiplexed signal, then to afirst amplifier 118 for amplifying the modulated signal, then to firstand second switches 119 and 120 for switching between the recording andplayback states; the other leading similarly to a second modulatingcircuit 121, a second amplifier 122, and third and fourth switches 123and 124.

The first through fourth switches 119, 120, 123, and 124 connect therecording section of the digital video tape recorder to first and seconddual rotary heads 125 and 126, which are installed in a drum 127. Eachdual rotary head 125 or 126 is capable of simultaneously scanning twohelical tracks in a segment on a tape 1. The first dual rotary head 125is connected to the first switch 119 and the third switch 123. Thesecond dual rotary head 126 is connected to the second switch 120 andthe fourth switch 124. The tape 1 wraps partly around the drum 127; inFIG. 20 the tape wrap angle is 180°.

The playback section 90 of this digital video tape recorder comprises afirst head switch 129 for selecting one of the dual rotary heads 125 and126, a fifth switch 130 for switching between the recording and playbackstates, a first playback amplifier 131 which receives the playbacksignal via these switches and amplifies it, a first demodulating circuit132 for demodulating the amplified signal, and similarly a second headswitch 133, a sixth switch 134, a second playback amplifier 135, and asecond demodulating circuit 136. The outputs of the first and seconddemodulating circuits 132 and 136 are applied to a separation circuit137 for separating the playback signal into a video signal and an audiosignal.

The separation circuit 137 Is connected to a playback audio digitalsignal processing circuit 138 which receives the audio signal andprovides outputs to a first number-of-playback-channels switch 139, asecond number-of-playback-channels switch 140, a first digital-to-analog(hereinafter written D/A) converter 141 for converting the channel-1audio signal to an analog signal, and similar second, third, and fourthD/A converters 142, 143, and 144 for channels 2, 3, and 4, respectively,the inputs to the third and fourth D/A converters 143 and 144 beingswitched by the first and second number-of-playback-channels switches139 and 140. The outputs of the first to fourth D/A converters 145 to148 are sent to a channel-1 audio signal output terminal 145, achannel-2 audio signal output terminal 146, a channel-3 audio signaloutput terminal 147, a channel-4 audio signal output terminal 148.

The video signal output from the separation circuit 137 sent to aplayback video digital signal processing circuit 149, then to a fifthD/A converter 150 for converting it to an analog signal, which is outputat a video signal output terminal 151.

FIG. 21 is a block diagram illustrating the detailed structure of theplayback audio digital signal processing circuit 138. The audio signalfrom the separation circuit 137 is applied to a decoding circuit 152 fordecoding the audio signal and detecting and correcting errors therein.Outputs from the decoding circuit 152 go to an ID detection circuit 153for detecting ID information in the audio signal, a first interpolationcircuit 154 for interpolating samples in channel 1, similar second,third, and fourth interpolation circuits 155, 156, and 157 for channels2, 3, and 4, a third number-of-playback-channels switch 158, and afourth number-of-playback-channels switch 159. The third and fourthnumber-of-playback-channels switches 158 and 159 are controlled by theID detection circuit 153, and select either the outputs of the first andsecond interpolation circuits 154 and 155 or outputs received from thedecoding circuit 152 for input to a first crossfading circuit 160 forcrossfading signals in channel 1 and a second crossfading circuit 161for crossfading signals in channel 2, respectively. The third and fourthinterpolation circuits 156 and 157 are connected directly to similarthird and fourth crossfading circuits 162 and 163 for crossfadingsignals in channels 3 and 4, respectively. The crossfading circuits 160to 163 also receive signals from the ID detection circuit 153. Thesignals output by the first and second crossfading circuits 160 and 161are applied directly to the first and second D/A converters 141 and 142,respectively. The signals output by the third and fourth crossfadingcircuits 162 and 163 are applied via the first and secondnumber-of-playback-channels switches 139 and 140 to the third and fourthD/A converters 143 and 144, respectively.

Next the normal recording operation of this digital video tape recorderwill be described for both the two- and four-channel cases. Duringrecording, the first, second, third, and fourth switches 119, 120, 123,and 124 are in the on state, connecting the recording section 80 to thedual rotary heads 125 and 126, and the fifth and sixth switches 130 and134 are set to the "Rec" position in FIG. 20, grounding the inputs tothe playback section 90.

For two-channel operation, audio signals are input at the channel-1audio signal input terminal 101 and the channel-2 audio signal inputterminal 102 in FIG. 20 and digitized by the first and second A/Dconverters 105 and 106. The first number-of-recording-channels switch109 and the second number-of-recording-channels switch 110 are both off,disconnecting the channel-3 and channel-4 inputs from the recordingaudio digital signal processing circuit 111. The recording audio digitalsignal processing circuit 111 thus receives the audio inputs forchannels 1 and 2, as well as information from the sequence circuit 112indicating that the input audio signal has two channels and that audiodubbing is not being performed.

For four-channel operation, audio signals are input at the channel-1audio signal input terminal 1, the channel-2 audio signal input terminal2, the channel-3 audio signal input terminal 3, and the channel-4 audiosignal input terminal 4 and digitized by the first, second, third, andFourth A/D converters 105, 106, 107, and 108. The firstnumber-of-recording-channels switch 109 and the secondnumber-of-recording-channels switch 110 are both on, so the recordingaudio digital signal processing circuit 111 receives audio input signalsfrom all four channels, as well as information from the sequence circuit112 indicating that the input audio signal has Four channels and thataudio dubbing is not being performed.

The recording audio digital signal processing circuit 111 separates theeven- and odd-numbered signal samples of the digitized audio signals,encodes them in an error-correcting code, adds the information from thesequence circuit 112 to the ID fields, and performs other processes,then sends the resulting audio signals to the mixing circuit 116.Meanwhile, the video signal is input at the video signal input terminal113, digitized by the fifth A/D converter 114, encoded in anerror-correcting code by the recording video digital signal processingcircuit 115, and likewise sent to the mixing circuit 116.

The mixing circuit 116 multiplexes the audio signals and the videosignal. The multiplexed signal is modulated by the first modulatingcircuit 117 and the second modulating circuit 121 and amplified by thefirst amplifier 118 and the second amplifier 122 to create the actualsignal to be recorded on the tape.

The signal is recorded on the tape 1 alternately by the first dualrotary head 125 and the second dual rotary head 126. During one 360°rotation of the heads, the first rotary head 125 scans the tape 1 forthe first 180°, recording two helical tracks in one segment, then thesecond rotary head 126 scans the tape 1 for the second 180°, recordingthe two helical tracks in the next segment. The signal for one of thetwo helical tracks in a segment comes from the first modulating circuit117 and first amplifier 118; the signal for the other helical track inthe same segment comes from the second modulating circuit 121 and secondamplifier 122.

The recording audio digital signal processing circuit 111, the recordingvideo signal processing circuit 115, and the mixing circuit 116 operateaccording to the novel recording method already described. Specifically,the recording audio digital signal processing circuit 111 processes theaudio signals one audio frame at a time, and the recording video digitalsignal processing circuit 115 processes the video signal one video frameat a time, the audio frames being offset by one field from the videoframes. In four-channel operation, the recording audio digital signalprocessing circuit 111 separates the even and odd samples of the audiosignals in an audio frame and outputs them into different fields in thatframe, each sample being recorded just once. In two-channel operation,the recording audio digital signal processing circuit 111 outputs theeven and odd samples separately into each field in the frame, eachsample being recorded twice, once in each field.

The outputs of the recording audio and video digital signal processingcircuits 111 and 115 and the mixing circuit 116 are timed so that theaudio signal is recorded in upper and lower tape edge audio sectors andthe video signal is recorded in video sectors as illustrated in FIGS. 8to 11. Details of this timing are omitted since they will be clear toone skilled In the art.

Next the normal playback operation of the digital video tape recorderwill be described for the two- and four-channel cases. Normal playbackrefers to the playback of a tape that has not been edited. Duringplayback, the first, second, third, and fourth switches 119, 120, 123,and 124 in FIG. 20 are in the off state, and time fifth and sixthswitches 130 and 134 are set to the "PB" position, so the first andsecond dual rotary heads 125 and 126 are connected to the playbacksection 90 of the digital video tape recorder and disconnected from therecording section 80.

In playback, the first head switch 129 and the second head switch 133 inFIG. 20 are switched to input the signal from the first dual rotary head125 and the second dual rotary head 126 alternately, the signal fromeach head being input while that head is scanning the tape 1. The signalthus read from the tape 1 is amplified by the first playback amplifier131 or the second playback amplifier circuit 136, demodulated by thefirst demodulating circuit 132 or the second demodulating circuit 136,then input to the separation circuit 137 and separated into an audiosignal and a video signal.

The video signal is input to the playback video digital signalprocessing circuit 149 which decodes it, corrects errors, and performsother processes, including a delay process to compensate for the longerprocessing time of the audio signal. The decoded video signal isconverted to an analog signal by the fifth D/A converter 150 and outputat the video signal output terminal 151.

The audio signal is input to the audio digital signal processing circuit138 where first the decoding circuit 152 decodes it and corrects errors,and the ID detection circuit 153 detects the ID information which wasadded by the sequence circuit 112 when the signal was recorded. Part ofthe ID information Indicates the number of channels. If the IDinformation indicates that there are four channels, the ID detectioncircuit 153 causes the third and fourth number-of-recording-channelsswitches 158 and 159 to select the outputs from the first and secondinterpolation circuits 154 and 155 for input to the first and secondcrossfading circuits 160 and 161. If the ID information indicates twochannels, the ID detection circuit 153 causes the third and fourthnumber-of-recording-channels switches 158 and 159 to select outputs fromthe decoding circuit 152 for input to the first and second crossfadingcircuits 160 and 161.

For a four-channel signal, if the decoding circuit 152 encounters anuncorrectable error In the even samples for channel 1, for example,commands from the decoding circuit 152 and ID detection circuit 153instruct the first interpolation circuit 154 to reconstruct those evensamples by interpolation from the odd samples. For a two-channel signal,which is recorded twice at different edges of the tape, if the decodingcircuit detects an uncorrectable error in one copy of the audio signalin channel 1, for example, commands from the decoding circuit 152 andthe ID detection circuit 153 instruct the first crossfading circuit 160to select the other copy. Errors in other channels are correctedsimilarly.

Since the tape has not been edited, no audio-dubbing flags are recordedin the ID fields. When the ID detection circuit 153 does not detect allaudio-dubbing flag, it directs the first, second, third, and fourthcrossfading circuits 160, 161, 162, and 163 not to perform crossfading.The audio signals thus pass through the crossfading circuits unalteredto the first and second D/A converters 141 and 142 and the first andsecond number-of-playback-channels switches 139 and 140.

The ID detection circuit 153 also controls the first and secondnumber-of-playback-channels switches 139 and 140, switching them on whenthere are four channels and off when there are only two channels. Thethird and fourth D/A converters 43 and 44 thus receive channels 3 and 4of a four-channel signal, and do not receive any input for a two-channelsignal. A four-channel audio signal is therefore output at the channel-1audio signal output terminal 145, the channel-2 audio signal outputterminal 146, the channel-3 audio signal output terminal 147, and thechannel-4 audio signal output terminal 148, while a two-channel audiosignal is output at the channel-1 audio signal output terminal 145 andthe channel-2 audio signal output terminal 146.

The novel digital video tape recorder thus uses the same record andplayback circuits to process both two- and four-channel audio signals,only simple switching operations being necessary to switch between thetwo- and four-channel modes. In playback, switching between two- andfour-channel operation is furthermore automatic, controlled by anumber-of-channels flag recorded in the audio signal. In four-channeloperation, the interpolation circuits can recover an audio signal evenif half of it is lost due, for example, clogging of one of the two dualrotary heads. In two-channel operation, a selection process performed inthe crossfading circuits provides the same protection without requiringinterpolation, enabling the audio signal to be recovered with no loss ofinformation. The ability of this digital video tape recorder to record atwo-channel audio signal twice at different edges of the tape, usingdifferent dual rotary heads, and select the signal from either edge inplayback makes both the recording and playback processes extremelyreliable.

Next the operation of the novel digital video tape recorder during audiodubbing will be described with reference to FIG. 22.

To dub a new audio signal onto a target tape, the operator begins byplaying back the target tape until he finds the video frame at which hewants to begin dubbing. During this phase the digital video taperecorder operates entirely in the playback mode, so that the existingaudio signal can be heard. The operator then switches to the dubbingmode, in which the digital video tape recorder inputs a new audio signaland records it in the audio sectors, overwriting the old audio signal,while continuing to play back the video signal from the video sectors.

FIG. 22 shows the transition from the playback mode to the dubbing modein more detail. The operator decides to start dubbing at the video frameincluding field n. The first audio frame is input while the dual rotaryheads are scanning fields n and n+1 and processed by the recording audiodigital signal processing circuit 111 while the heads are scanningfields n+2 and n+3, the data thus generated being output from therecording section of the digital video tape recorder while the heads arescanning fields n+4 and n+5. Recording, however, does not begin untilthe video frame comprising fields n+5 and n+6.

Specifically, the digital video tape recorder switches briefly to therecording mode to record the audio sectors located at the end of fieldn+5 and the beginning of field n+6. For a four-channel audio signal, theodd samples of the first audio frame are recorded in field n+5. For atwo-channel audio signal, boll, the even and odd samples of the firstaudio frame are recorded in field n+5. To mark the transition from theold audio signal to the new, the sequence circuit 112 adds anaudio-dubbing flag to the ID information recorded in field n+5.

The next new audio signal frame is input while the dual rotary heads arescanning fields n+2 and n+3, processed in fields n+4 and n+5, and outputand recorded in fields n+6 and n+7. For a four-channel audio signal, theeven samples are recorded in field n+6 and the odd samples in field n+7.For a two-channel audio signal, the entire signal is recorded once inframe n+6 and once again in frame n+7. Audio dubbing continues in thisway, each audio frame being recorded in two fields, which are located inseparate video frames.

If the operator decides to stop audio dubbing after four video frames,for example, then the last audio frame is recorded in field n+10 but notin field n+11. For a four-channel audio signal, the even samples of thelast audio frame are recorded in field n+10. For a two-channel audiosignal, both the even and odd samples of the first audio frame arerecorded once in field n+10. The sequence circuit 112 records anotheraudio-dubbing flag in the ID information in field n+10.

Next the playback of an edited tape will be described. For frames inwhich no audio-dubbing flag is detected, playback of an edited tape isthe same as the normal playback process, so the description will belimited to audio frames in which an audio-dubbing flag is recorded.Separate descriptions will be given for the two-and four-channel cases.

In the four-channel case, when the ID detection circuit 153 detects anaudio-dubbing flag, it commands the first, second, third, and fourthinterpolation circuits 154, 155, 156, and 157 to interpolate the twofields of the current audio frame separately, thereby generating the oldaudio signal from one field and the new audio signal from the otherfield. The first, second, third, and fourth crossfading circuits 160,161, 162, and 163 are commanded to crossfade the old audio signal withthe new audio signal in this frame. The result is the operationillustrated in FIGS. 18A and 18B, providing a smooth transition from theold audio signal to the new, or from the new audio signal to the old.

In the two-channel case, when the ID detection circuit 153 detects anaudio-dubbing flag, it commands the first and second crossfadingcircuits 161 and 162 to crossfade the two fields of the current audioframe, which are obtained directly from the decoding circuit 152 In thiscase. Since one field contains the complete old audio signal and theother field contains the complete new audio signal, the result is againa smooth transition between the old and new audio signals, asillustrated in FIGS. 19A and 19B.

By marking audio dubbing with an audio-dubbing flag recorded at the editpoints and crossfading the old and new audio signals when this flag isdetected during playback, the novel digital video tape recorder createsa natural transition between the old and new audio signals, withoutrequiring external noise countermeasures.

The scope of this invention is not limited to the embodiments shown inthe preceding drawings, but includes numerous modifications andvariations which will be obvious to one skilled in the art. For example,the audio and video frames can be divided into more than two fieldseach, as long as an appropriate offset is provided between the audio andvideo frames. The audio signal can be recorded in more than two segmentsper frame. Furthermore, the audio sectors need not be located near theedges of the tape, as long as they are located in different positionswith respect to the width of the tape. The crossfade time need not belimited to one frame at the edit points; the new and old audio signalscan be crossfaded for two or more audio frames to provide an evensmoother transition between them. Audio dubbing flags can be recordednot just during audio dubbing but in any type of editing that replacesan old audio signal with a new audio signal. Moreover, audio dubbingflags can be recorded in all dubbed audio fields instead of just thefirst and last, in which case the new audio signal may be crossfadedwith itself in interior audio frames.

What is claimed is:
 1. A digital signal recording method for recordingdigital multi-channel audio and video signals in helical tracks on atape, comprising the steps of:(a) recording the video signal in videosectors in the helical tracks; (b) for each of the audio channels,separating even samples from odd samples of the audio signal associatedwith each channel; (c) recording the even samples of the audio signal inaudio sectors of first tracks disposed near one edge of the tape; and(d) recording the odd samples of the audio signal in audio sectors ofsecond tracks disposed near the other edge of the tape, the secondtracks on which the odd samples are recorded being different from thefirst tracks on which the even samples are recorded in step (c).
 2. Themethod of claim 1, further comprising the step of:(e) recordinginformation indicating the number of audio channels in the audiosectors.
 3. The method of claim 1, wherein said steps (c) and (d) recordsamples of the audio signal in audio frames and said step (a) record thevideo signal in video frames, the audio frames beginning at a differenttime than the video frames such that boundaries between the audio framesare offset from boundaries between the video frames, the helical trackscontaining the odd and even samples being located in different videoframes.
 4. The method of claim 3, wherein when the audio signal isrecorded by audio dubbing, an audio-dubbing flag is recorded in at leastthe first and last audio frames in which audio dubbing is performed. 5.The method of claim 1 wherein the even and odd samples of a single audioframe recorded by said steps (c) and (d) are recorded during differentvideo frames on the tape as recorded by said step (a).
 6. The method ofclaim 1 wherein said steps (c) and (d) record an even sample and an oddsample of the audio signal in an audio sector on the end of each trackadjacent one edge of the tape.
 7. The method of claim 6 wherein thehelical tracks are arranged in track pairs of adjacent tracks, the trackpairs having the audio sectors thereof disposed near the same edge ofthe tape.
 8. The method of claim 7 wherein adjacent track pairs havingaudio signals provided thereon have their associated audio sectorsdisposed near opposite edges of the tape so that alternate track pairshaving audio signals provided thereon have their associated audiosectors disposed on the same edge of the tape.
 9. The method of claim 8wherein a single audio frame is formed by a pair of track pairs (fourtracks) separated by tracks containing only video signals.
 10. Themethod of claim 9 wherein the even samples of two channels are eachdisposed on outer ones of two subsectors of each track of a first trackpair while the odd samples of the other two channels are each disposedon outer ones of two subsectors of a second track pair adjacent to thefirst track pair.
 11. The method of claim 9, wherein the audio signalcomprises four channels, the audio sectors of adjacent track pairs eachcomprising two audio subsectors, the even samples of two of the channelsand the odd samples of the other two channels being recorded in theaudio subsectors of adjacent track pairs disposed nearest the edge ofthe tape.
 12. The method of claim 9 wherein the audio signal comprisestwo channels and said steps (c) and (d) respective even and odd samplesare performed twice for each audio frame, the even samples beingrecorded near one edge of the tape the first time, and near the otheredge of the tape the second time.
 13. The method of claim 12, whereinrespective audio subsectors comprise forty-eight data blocks, eachcomprising a forty-byte data or C2 field in which data or an outererror-correcting code is recorded, and a two-byte C1 field which isrecorded an inner error-correcting code for correcting errors within thedata block.
 14. The method of claim 13, wherein said data or C2 fieldseight of said forty-eight data blocks contain outer error-correctingcodes for correcting errors extending across said data blocks.
 15. Themethod of claim 12, wherein respective audio subsectors comprise thirtydata blocks, each comprising an eighty-byte data or C2 field in whichdata or an outer error-correcting code is recorded, and an eight-byte C1field in which is recorded an error-correcting code for correctingerrors within the data block.
 16. The method of claim 15, wherein saiddata or C2 fields in ten of said thirty data blocks contain outererror-correcting codes for correcting errors extending across said datablocks.
 17. The method of claim 12 wherein a single audio frame isformed by a pair of track pairs (four tracks) separated by trackscontaining only video signals.
 18. The method of claim 17, whereinrespective audio subsectors comprise thirty data blocks, each comprisingan eighty-byte data or C2 field in which data or an outererror-correcting code is recorded, and an eight-byte C1 field in whichis recorded an error-correcting code for correcting errors within thedata block.
 19. The method of claim 18, wherein said data or C2 fieldsin ten of said thirty data blocks contain outer error-correcting codesfor correcting errors extending across said data blocks.
 20. The methodof claim 17, wherein respective audio subsectors comprise forty-eightdata blocks, each comprising a forty-byte data or C2 field in which dataor an outer error-correcting code is recorded, and a two-byte C1 fieldin which is recorded an error-correcting code for correcting errorswithin the data block.
 21. The method of claim 20, wherein said data orC2 fields in eight of said forty-eight data blocks contain outererror-correcting codes for correcting errors extending across said datablocks.
 22. The method of claim 21 wherein the tracks having audioinformation recorded thereon are arranged in track pairs, a track pairhaving a sample of the audio information of each channel recordedthereon.
 23. The method of claim 22 wherein even samples of two of thechannels and the odd samples of the other two channels are recorded inthe audio subsectors of one track pair.
 24. The method of claim 22wherein adjacent track pairs having audio signals provided thereon havetheir associated audio sectors disposed near opposite edges of the tapeso that alternate track pairs having audio signals provided thereon havetheir associated audio sectors disposed on the same edge of the tape.25. The method of claim 24 wherein a single audio frame is formed by apair of track pairs (four tracks) separated by tracks containing onlyvideo information.
 26. A digital video tape recorder for recordingdigital multi-channel audio and video signals on a tape and playing backrecorded signals, comprising:a recording audio digital signal processingcircuit for receiving digital audio signals associated with each of themulti-channels, separating the digital audio signals associated witheach channel into even and odd samples, and encoding each of saidsamples as digital data; a recording video digital signal processingcircuit for receiving a video signal and encoding it as digital data; amixing circuit for receiving outputs of said recording audio digitalsignal processing circuit and said recording video digital signalprocessing circuit and multiplexing the outputs to generate a pair ofmultiplexed signals; a pair of modulating circuits for receiving saidmultiplexed signals and modulating the received multiplexed signals togenerate a pair of modulated signals; rotary head means for receivingsaid pair of modulated signals and recording said pair of modulatedsignals on helical tracks of said tape, said rotary head means recordingeven samples of the audio signals on one edge of the tape and oddsamples of the audio signals on the other edge of the tape, said evensamples being recorded in different tracks from said odd samples, saideven and odd samples being recorded on less than all of the tracksmaking up a video frame, said rotary head means further reading signalsfrom the tape to generate a pair of playback signals; a pair ofdemodulating circuits for receiving said pair of playback signals anddemodulating said pair of playback signals to generate a pair ofdemodulated signals; a separation circuit for receiving said pair ofdemodulated signals and separating said pair of demodulated signals intoaudio and video signals; a playback video digital signal processingcircuit for receiving said video signal from said separation circuit,decoding said video signal, and generating an output video signal; and aplayback audio digital signal processing circuit comprising a decodingcircuit for receiving said audio signals from said separation circuit,decoding said audio signals, and generating a decoded audio signalassociated with each audio channel, and one or more interpolationcircuits connected thereto, said interpolation circuits receiving saiddecoded audio signals and regenerating the audio signal for each channelfrom half of its samples by interpolating either the even samples or theodd samples when an error is present.
 27. The digital video taperecorder of claim 26, further comprising:a sequence circuit forgenerating an audio-dubbing flag and sending it to said recording audiodigital signal processing circuit for recording in an ID field in saidaudio signal; an ID detection circuit disposed in said playback audiodigital signal processing circuit, connected to said decoding circuitand said interpolation circuits, for receiving said decoded audiosignal, detecting said audio dubbing flag and, when said audio dubbingflag is detected, generating commands instructing said interpolationcircuits to interpolate both even and odd samples thereby generating oldand new audio signals; and one or more crossfading circuits disposed insaid playback audio digital signal processing circuit, connected torespective interpolation circuits and to said ID detection circuit, forreceiving said old and new audio signals from respective interpolationcircuits and crossfading them on command from said ID detection circuitwhen said audio dubbing flag is detected.
 28. The digital video taperecorder of claim 27, wherein said sequence circuit generates a flagindicating the number of channels in said audio signal and sends it tosaid recording audio digital signal processing circuit for recording insaid ID field in said audio signal.
 29. The digital video tape recorderof claim 28, further comprising at least one number-of-channels switch,disposed between at least one interpolation circuit and at least onecrossfading circuit and also connected to said decoding circuit, forselecting the output of said decoding circuit or said interpolationcircuit as the input to said crossfading circuit, said selection beingmade according to the number of audio channels in said audio signal. 30.A method of digitally recording audio and video information on a tapecomprising the steps of:(a) recording video information as video signalson tracks across the tape, individual video images being stored in videoframes, respectively, each video frame having more than one track; (b)recording sequentially sampled audio information as odd and even samplesof audio signals on tracks across the tape, audio signals correspondingin time to said video images are stored in audio frames, respectively;and (c) arranging at least some of the tracks to contain part of both avideo frame and an audio frame and having video and audio signalsrecorded thereon; said step (b) recording audio information such thatthe audio frames begin at a different time than the video frames andboundaries of the audio frames are offset from the boundaries of thevideo frames by half the distance between the boundaries of the videoframes; said step (b) recording audio information such that trackscontaining the odd and even samples of the audio signal are located indifferent video frames; said step (b) recording by interleaving theaudio frame with the video frame so that audio signals of an audio frameare on tracks of more than one video frame, thereby enabling improvedaudio dubbing.
 31. The method of claim 30 further comprising the stepsof:(d) digitalizing the audio information into a plurality of digitalaudio samples; and (e) separating the digitalized audio samples into oddsamples and even samples.
 32. The method of claim 31 wherein said step(b) divides each audio frame substantially equally between tracks whichare part of adjacent video frames.
 33. The method of claim 30 whereineach audio frame includes both even samples and odd samples, and foreach audio frame, the even samples and odd samples being provided indifferent video frames.
 34. The method of claim 33 wherein the audiosignals are recorded in audio sectors of individual tracks.
 35. Themethod of claim 34 wherein the tracks having audio information recordedthereon are arranged in track pairs, a track pair having a sample ofeach channel recorded thereon.
 36. The method of claim 35 wherein evensamples of two channels and the odd samples of another two channels arerecorded in the audio subsectors of one track pair.
 37. The method ofclaim 36 wherein adjacent track pairs having audio signals providedthereon have their associated audio sectors disposed near opposite edgesof the tape so that alternate track pairs having audio signals providedthereon have their associated audio sectors disposed on the same edge ofthe tape.
 38. The method of claim 30 wherein said steps (a) and (b)helically record the tracks on the tape.
 39. The method of claim 30wherein the audio information includes four channel sound information,said step (b) records four channel sound information on the tape usingerror correction coding but without any audio information redundancy.40. The method of claim 30 wherein said step (a) records the videosignals on all the tracks.
 41. The method of claim 30 wherein said step(b) records the audio information on only one end of each trackcontaining audio information.
 42. A system for digitally recording audioand video information on a tape comprising:first means for recordingvideo information as video signals on tracks across the tape, individualvideo images being stored in video frames, respectively, each framehaving more than one track; and second means for recording sequentiallysampled audio information as odd and even samples of audio signals ontracks across the tape, audio signals corresponding in time to saidvideo images are stored in audio frames, respectively, such that theaudio frames being at a different time than the video frames andboundaries of the audio frames and boundaries of the video frames areoffset by half the distance between the boundaries of the video frames,and such that tracks containing the odd and even samples of the audiosignal are located in different video frames; at least some of saidtracks being part of both a video frame and an audio frame and havingvideo and audio signals recorded thereon; and said second meansrecording by interleaving said audio frame with said video frame so thataudio signals of an audio frame are on tracks of more than one videoframe, thereby enabling improved audio dubbing.
 43. The system of claim42 further comprising:means for digitalizing said audio information intoa plurality of digital audio samples; and means for separating saiddigitalized audio samples into odd samples and even samples.
 44. Thesystem of claim 42 wherein each audio frame includes both even samplesand odd samples;for each audio frame, said even samples and odd samplesbeing provided in different video frames.
 45. The system of claim 42wherein said first and second means helically record said tracks on saidtape.
 46. The system of claim 42 wherein said audio information includesfour channel sound information, said second means recording said fourchannel sound information on said tape using error correction coding butwithout any audio information redundancy.
 47. The system of claim 42wherein said first means records said video signals on all said tracks.48. The system of claim 42 wherein said second means records said audioinformation on only one end of each track containing audio information.49. A method of audio dubbing in a digital audio and video storagesystem comprising the steps of:(a) recording audio and video informationin audio and video frames respectively on a storage medium, with thevideo frames representing individual video images, respectively, theaudio frames corresponding in time to said individual video images,respectively, and the audio information of each audio frame beingdivided into odd and even samples; said step (a) recording the audio andvideo information on tracks of a tape in an interleaved fashion so thatthe odd and even samples are stored on tracks within different videoframes and each video frame has odd and even samples of different audioframes associated therewith with an audio frame beginning within eachvideo frame, the audio frames beginning at a different time than thevideo frames such that boundaries of the audio frames and boundaries ofthe video frames are offset by half the distance between the boundariesof the video frames; (b) selecting a video frame at which to beginreplacing stored audio information with replacement audio information toform a selected audio dubbing point; (c) replacing the audio frame whichbegins within the selected video frame with a replacement frame ofreplacement audio information so that at least one odd or even sample ofthe originally stored audio frame and at least one odd or even sample ofthe replacement frame remain associated with the selected video framethereby allowing crossfading between the stored audio information andthe replacement audio information to improve the dubbed audio track bysmoothing the transition between the stored and replacement audioinformation; and (d) continuing the replacing of audio frames asdesired.
 50. The method of claim 49 wherein said method is further animproved reproduction method further comprising the steps of:(e) readingthe stored audio and video information from the storage medium includingreading the video frames and the audio frames; (f) at each selectedaudio dubbing point, reading the remaining odd or even samples of theoriginally stored audio frame and the odd or even samples of thereplacement frame of replacement audio information; and (g) at eachselected dubbing point, smoothing the remaining odd or even samples ofthe originally stored audio frame and the odd or even samples of thereplacement frame of replacement audio information to crossfade betweenthe original stored audio information and the replacement audioinformation to avoid an abrupt edge therebetween.
 51. The method ofclaim 50 wherein the selected dubbing point is marked with an audiodubbing flag stored on the storage medium.
 52. The method of claim 49wherein the odd or even samples of the replacement frame of thereplacement audio information are complementary to the remaining odd oreven samples of the originally stored audio frame at the selecteddubbing point.
 53. A system for audio dubbing in a digital audio andvideo storage system comprising:recording means for recording audio andvideo information in audio and video frames respectively on a storagemedium, with said video frames representing individual video images,respectively, the audio frames corresponding in time to said videoimages, respectively, and the audio information of each audio framebeing divided into odd and even samples; said recording means recordingsaid audio and video information on tracks of a tape in an interleavedfashion so that the said odd and even samples are stored on trackswithin different video frames and each video frame has odd and evensamples of different audio frames associated therewith with an audioframe beginning within each video frame; means, responsive of theselection of a video frame at which to begin replacing stored audioinformation with replacement audio information to form a selected audiodubbing point, for replacing audio frames as desired beginning withreplacing the audio frame which begins within the selected video framewith a replacement frame of replacement audio information so that atleast one odd or even sample of the originally stored audio frame and atleast one odd or even sample of the replacement frame remain associatedwith the selected video frame, thereby allowing crossfading between thestored audio information and the replacement audio information toimprove the dubbed audio track by smoothing the transition between thestored and replacement audio information.
 54. The system of claim 53wherein said system is further an improved reproduction system furthercomprising:playback means for reading said stored audio and videoinformation from the storage medium including reading said video framesand said audio frames; said playback means reading, at each selectedaudio dubbing point, the remaining odd or even samples of the originallystored audio frame and the odd or even samples of the replacement frameof replacement audio information; and crossfade means for smoothing, ateach selected dubbing point, the remaining odd or even samples of theoriginally stored audio frame and the odd or even samples of thereplacement frame of replacement audio information to crossfade betweenthe original stored audio information and the replacement audioinformation to avoid an abrupt edge therebetween.
 55. The system ofclaim 53 wherein said selected dubbing point is marked with an audiodubbing flag stored on said storage medium.
 56. The system of claim 53wherein said odd or even samples of the replacement frame of thereplacement audio information are complementary to the remaining odd oreven samples of the originally stored audio frame at the selecteddubbing point.
 57. A digital signal recording apparatus for recordingdigital multi-channel audio and video signals in helical tracks on atape comprising:video recording means for recording the video signal invideo sectors in the helical tracks; separating means, for each of theaudio channels, for separating even samples from odd samples of theaudio signal associated with each channel; audio recording means forrecording even samples of the audio signal in audio sectors of firsttracks disposed near one edge of the tape and for recording said oddsamples of the audio signal in audio sectors of second tracks disposednear the other edge of said tape, said second tracks on which said oddsamples are recorded being different from said first tracks on whichsaid even samples are recorded.